Synthesis of polyamimes, which are essential to tissue growth and proliferation, is sensitively controlled by the activity of the enzyme, ornithine decarboxylase. The mechanism of regulation of this enzyme will be investigated in a simple eukaryote, Physarum polycephalum, which has a polyamine synthetic pathway similar to mammalian systems, yet is much more amenable to biochemical manipulation. Enzyme literature and preliminary work indicate that the variable interaction of the ornithine decarboxylase apoenzyme with its coenzyme, pyridoxal-5-phosphate, may be central to the control of activity, yet this enzyme characteristic has not yet been investigated. Variations in the ability of added coenzyme to stimulate enzyme activity in vitro will be studied as they correlate with activity changes in vivo, when induced by inhibitors, altered growth conditions, or natural developmental alterations. Changes in enzyme structure or conformation, which result in the decreased affinity for coenzyme, will be investigated using column chromotography, gel electrophoresis, amino acid analyzer and gradient centrifugation techniques. Factors influencing coenzyme-enzyme interactions will be sought, and evaluated for their ability to regulate this enzyme. Such factors, provided they are incorporated and effectual in living tissue, may be utilized to expand our understanding of the role of polyamines in embryonic development and diseases, such as cancer and cystic fibrosis, which are associated with elevated polyamine levels. BIBLIOGRAPHIC REFERENCES: John L.A. Mitchell, Regulation of Ornithine Decarboxylase Activity in Physarum; American Society of Cell Biology Abstracts for the l974 meeting. John L.A. Mitchell and Mark J. Sedory (1974) Cycloheximide induced modification of ornithine decarboxylase in Physarum polycephalum, FEBS Letters 49, 120-124.